New Suggestion
In the website https://app.sleekplan.com/settings/designer/page/4 until last week, I inserted my custom style on the Custom HTML > Head section and it was working perfectly, today I see that I can now set a custom CSS in the Custom HTML > Custom CSS section, but now my personalised style it's not working on either of these sections. In the HTML sections, it says that I'm including JavaScript code, when I am not, no matter what I write. And in the CSS, I write it, it saves, but it doesn't overwrite the current CSS of the preview page (Edit: later tested it and Custom CSS does make effect on the published version of the page for end-users, but not on the preview).
You can try it yourselves, if you need to try it in my account, you can contact me freely. The "Custom HTML" in the page designer is just not working at all.
Using a custom domain in https://app.sleekplan.com/settings/widget/page configuration
@david_nortes for styles you have to use the "custom CSS" section. The head section only allows for external CSS like
<link rel="stylesheet" href=...>
or scripts like<script src=...>
@marco thanks for the reply. Yes, now I tried it on the Custom CSS as expected from you (I just didn't use it before because I didn't see it there). It is working for end-users on the published page, but I can't see it on the preview, could you check that? Right now I can make use of this and it works, so it's not that important, but seeing the changes on the preview would be great ;) Thanks in advance!!
@david_nortes Thanks for the hint. We have shipped a fix for that! 😊